1. Field of the Invention
The present invention relates to a worm speed change apparatus having a worm shaft and a worm wheel to be meshed therewith, and also relates to an electric power steering apparatus comprising this worm speed change apparatus.
2. Description of Related Art
Generally, an electric power steering apparatus is arranged such that a steering assistance electric motor is reduced in the number of rotations through a speed reducer and that the resulting reduced rotational force is transmitted to a steering mechanism such as a rack-and-pinion mechanism or the like. A worm speed reducer is often used as the above-mentioned speed reducer.
In a worm speed reducer, both ends of the worm shaft meshed with the worm wheel serving as a speed reduction gear, are rotatably supported by a housing through respective bearings each comprising inner and outer rings and rolling elements.
In such an arrangement, the worm shaft, the inner rings, the rolling elements and the outer rings are disposed in the diametral direction of the worm shaft. This disadvantageously increases not only the number of component elements, but also the size in the diametral direction of the worm shaft in its entirety. Further, while the worm shaft is under rotation, its axis disadvantageously easily swings transversely due to the increased number of component elements.